In various semiconductor fabrication processes, the effluent gases from a process chamber must be treated before they can be released into a factory exhaust system and into the atmosphere. It is known that a large number of reactant gases and their reaction products utilized in the semiconductor fabrication processes are either highly flammable or highly toxic. The spent reactant gases that are discharged out of the process chamber may contain gases that have not been reacted or have been only partially reacted and therefore must be treated before they can be released into the atmosphere.
In a semiconductor fabrication facility, the treatment of the exhaust gases generated from the facility is an important aspect of the total fabrication processes. Various exhaust gases are produced in a semiconductor fabrication facility, these include general exhaust, scrubbed exhaust and solvent exhaust. For discharging the general exhaust and the solvent exhaust, a system typically includes ductworks, exhaust fans, by-passes, and stacks can be used. For handling the scrubbed exhaust, a scrubber must be used for treating the exhaust before they can be released into the atmosphere. A by-pass system can be provided which allows the drawing of outside air when the pressure at the suction side of the blower exceeds a preset value.
In a general exhaust system, heat dissipated by the process equipment is normally removed. The general exhaust therefore does not normally contain acids, caustics or solvents. In a solvent exhaust system air containing solvents from the process equipment is removed. The devices utilized in the exhaust system therefore must be explosion-proof for safety reasons. In the scrubbed exhaust system, air containing acids, caustics and other harmful chemicals from the process chamber is removed. Various caustics in the exhaust gases such as ammonia, silane or other toxic gases must be treated by a scrubber before releasing into the atmosphere. A wet scrubber is normally used to remove acids and caustics in a process chamber exhaust by washing the air with a solvent such as water. City water is adequate for such purpose. The waste water from the scrubber is then sent to a neutralization plant in a waste treatment area of the fabrication facility. A dry scrubber can also be used to remove caustics substances from a process chamber exhaust by absorbing the substances into a scrubber material which is typically maintained at an elevated temperature. The scrubber material can then be replaced when it is saturated with the toxic substances.
The various exhaust systems are connected to process machines via ductworks. For instance, when exhausting from a metal etcher, a chemical vapor deposition chamber or a sputter, spent reactant gases and reaction by-products are normally discharged into a scrubbed exhaust system for treatment before the exhaust can be released to the atmosphere. A typical system for treating exhaust gases from a semiconductor process chamber such as an etcher is shown in FIG. 1.
Referring initially to FIG. 1, wherein a semiconductor fabrication system 10 is shown. The fabrication system 10 consists of an etcher 12, a vent exhaust 14, a main booster pump 16, a dry pump 22, a nitrogen purge gas supply 24 and a wet scrubber 26. Into the metal etcher 12, carrier gases and etchant gases (not shown) are first fed into the chamber through various valve openings (not shown). An inert gas such as pure nitrogen is normally used either as a carrier gas for the etchant gases or as a purge gas when venting of the chamber to atmospheric pressure is needed. In a typical metal etching, application, etchant gases such as Cl.sub.2 and BCl.sub.3 are used. In a batch-type metal etcher where a plurality of wafers, i.e., 16 wafers in a column type etcher, are etched in a typical etching process. In order to achieve an effective etching rate for a large number of wafers, a high concentration of etchant gas must be utilized in the etch chamber 12. The exhaust gases discharged from the etcher 12 at the outlet port 18 therefore contains a high concentration of un-spent etchant gases and other etching reaction by-products. The vent exhaust 14 is provided for venting of the pure nitrogen used to purge out the etch chamber 12 after an etching reaction. The un-spent etchant gases are discharged out of the etching chamber 12 by the main booster pump 16. A dry pump 22 is subsequently used to deliver the un-spent etchant gases into a wet scrubber 26 through an inlet port 20.
The pump exhaust system 30 which includes the main booster pump 16 and the dry pump 22, and the dry nitrogen source 24 are controlled by a series of valves (not shown). When the valves between the etcher 12 and the main booster pump 16 are opened, exhaust gases exit outlet port 18 and pass through the passageway 28 to enter into the main booster pump 16. The main booster pump 16 acts as the front stage pump and the dry pump 22 acts as the back stage pump, which work together to provide a vacuum that is sufficiently high for the etch chamber 12 prior to an etching process. The exhaust gases exit the dry pump 22 through passageway 34 and enter the wet scrubber 26 through an inlet port 20. During a normal etching process, chamber 12 is first evacuated by the operation of the main booster pump 16 and the dry pump 22 to a suitable vacuum for conducting the etching process. Etchant gases then enter into the chamber to commence the etching process on the wafers. A suitable chamber pressure is maintained during such etching process.
FIG. 2 is a schematic illustrating a detailed view of the exhaust gas conduit 34 and the wet scrubber 26 shown in FIG. 1. It is seen that exhaust gases 38 delivered from the dry pump 22 enter inlet 42 of the exhaust gas conduit 34. The exhaust gas conduit 34 is normally constructed of stainless steel such that it can be maintained at an elevated temperature of approximately 120.degree. C. by the heaters 44 to reduce the potential of particulate depositions in the conduit 34. As the exhaust gases 38 enters the wet scrubber 26 through the inlet port 20, the exhaust gases 38 are washed by a cleaning solvent 48 dispensed from a spray head 50. The cleaning solvent 48 is first supplied from a solvent reservoir (not shown) through conduit 52. A commonly used cleaning solvent for a wet scrubber is city water. After being scrubbed by the cleaning solvent 48, the exhaust gases 38 exit the wet scrubber 26 through an exhaust outlet port 46 into a factory exhaust system (not shown). The spent cleaning solvent 48 is collected by the solvent collection device 54 and then transported through conduit 56 into a spent solvent collection tank 58.
It should be noted that, in the application of a wet scrubber for a metal etcher, the spent water collected in the collection tank 58 is maintained at a pH value between about 6 and about 6.3. In other words, the spent city water is allowed to be slightly acidic after it is used to scrub the exhaust gases. The effectiveness of the wet scrubbing operation is maintained by continuously adding fresh city water to the spent water collection tank 58 and recirculating the water through the scrubbing process as long as the pH value of the spent water is between the values described above.
A major problem in the operation of the exhaust gas conduit in connection with the wet scrubber shown in FIG. 2 has been observed. The problem occurs at the outlet end 40 of the exhaust gas conduit 34, specifically on the inside wall 36 of the outlet end 40 immediately adjacent to the inlet port 20 on the wet scrubber 26. As previously described, the walls of the stainless steel exhaust gas conduit 34 are heated by heaters 44 to maintain the walls at an elevated temperature such that deposition of solids on the inside wall 36 can be avoided. However, at the interface between the outlet end 40 of the exhaust gas conduit 34 and the inlet port 20 of the wet scrubber 26, there is a substantial temperature drop due to the fact that the city water spray 48 inside the wet scrubber chamber 68 substantially drops the chamber temperature to at or below room temperature. The lower temperature region at the interface between the inlet port 20 and the outlet end 40 therefore provides a location for the deposition of solids precipitated from the exhaust gases 38. The solid deposit 64, shown in FIG. 2, accumulates to the stage that the deposit either partially blocks the inlet port 20 or completely blocks it. This creates a serious processing problem in that the exhaust gases 38 can not longer enter the wet scrubber 26 resulting in the need for a complete disassembly of the exhaust gas conduit 34 from the wet scrubber 26 in order to remove the solid deposit 64 from the outlet end 40 of the conduit 34. Such maintenance procedure creates unnecessary down time and therefore greatly reduces the yield of the metal etcher 12.
It is therefore an object of the present invention to provide an exhaust gas conduit for feeding an exhaust gas to a scrubber that does not have the drawbacks or shortcomings of the conventional exhaust gas conduits.
It is another object of the present invention to provide an exhaust gas conduit for feeding an exhaust gas to a scrubber that is equipped with a self-cleaning device mounted inside the conduit body and adjacent to an outlet and of the conduit for dispensing a cleaning solvent to the inside wall of the conduit.
It is a further object of the present invention to provide an exhaust gas conduit for feeding an exhaust gas to a scrubber that is equipped with a self-cleaning device inside the conduit body for spraying a cleaning solvent on the inside wall of the conduit and thus preventing solid deposition thereon.
It is another further object of the present invention to provide an exhaust gas conduit for feeding an exhaust gas to a wet scrubber by providing a self-cleaning device inside the conduit and mounted to a 90.degree. bent at an outlet end of the conduit such that solid deposition at the outlet end can be eliminated or minimized.
It is yet another object of the present invention to provide a wet scrubber for treating an exhaust gas from a process chamber by equipping the wet scrubber with an exhaust gas conduit for feeding an exhaust gas to the wet scrubber wherein the exhaust gas conduit is equipped with a self-cleaning device for spraying a cleaning solvent on the inside wall of the conduit and thus preventing solid formation on the inside wall and any possible blockage of the conduit.
It is still another object of the present invention to provide a wet scrubber for treating an exhaust gas from a process chamber by providing a self-cleaning device inside an exhaust gas conduit consists of a spray nozzle and a cleaning solvent conduit such that a cleaning solvent can be sprayed from the spray nozzle to prevent solid deformation inside the conduit.
It is still another further object of the present invention to provide a method for preventing solid deposition in an exhaust gas inlet port to a wet scrubber by attaching an exhaust gas conduit to the exhaust gas inlet port which is equipped with a self-cleaning device inside the conduit for spraying a cleaning solvent such that solid deposition inside the conduit passage can be substantially eliminated.
It is yet another further object of the present invention to provide a method for preventing solid deposition in an exhaust gas inlet port to a wet scrubber by installing a self-cleaning device on the inside of the conduit which has at least one spray head adapted for spraying a cleaning solvent onto an inside wall of the conduit such that any deposition of solids on the inside wall can be avoided.